477. Bombs are sometimes fired with a port fire stuck into the fuze-hole, which is an almost certain mode of igniting many kinds of buildings.
478. Mortars can also be fired with a bag of one-pound balls, or ordinary grape-shot, with very reduced charges, and a wad between the powder and the balls. One pound of powder will project a 200-lb. bomb 302 yards; the same weight of grape-shot thrown in among boats would prove destructive; and especially a lot of canister fired in this manner would cause great havoc.
479. It is not expected, however, that much execution could be done after the first discharge in a fleet of boats moving rapidly; but combined with the batteries of the Squadron, it is presumed that an enemy would be deterred from an attempt to capture a vessel by boarding.
TAKING THE DISTANCE.
480. An inexperienced officer will find difficulty in estimating distances by the eye alone, as it requires long practice and studied observation. The sextant, however, offers a surer method of approximately fixing a position by taking the angles between any three points, which are generally found to be accurately laid down on the Coast Survey charts; then plotting the angles with a horn protractor, or working them out by the three-point problem, which is given in all surveying books.
481. If the object to be assaulted is a large one, a practical man can, by the exercise of moderate judgment after two or three fires, throw the bombs near the work; but, at the same time, the sextant is the more certain means for determining the true distance, and the Officer in command should make himself acquainted with the simple manner of measuring horizontal angles.
482. If points are not visible in line, then measure a base on shore, angle on the object to be aimed at, and from the angles of the base-line, you can fix the position of the mortar-vessel.
483. When a vessel once gets her position accurately determined, and it becomes necessary after a bombardment to remove out of the line of battle, a small buoy with the vessel's name or number should be dropped under foot, so that the same position may, if necessary, be resumed.
LOADING MORTARS.
484. After the powder has been emptied through the funnel out of the cotton bag into the chamber, the bomb, loaded and fuzed, is to be carefully lowered into the bore by the hooks, and allowed to rest upon the charge.